In many cases, integrated-circuit devices are embedded in a solid-body package. One popular package, for example, is the plastic quad flat package (QFP), which has so-called gull-wing leads extending from the four sides of the generally planar, rectangular package. With this type of package, an integrated-circuit device is bonded to a package substrate, using an epoxy material. The package substrate may be the die paddle portion of a lead-frame, for example. Wire bonds are attached from bond pads on the device to attachment points on package leads. The device and the package substrate are then over-molded with a plastic molding compound material, which, after curing, forms the plastic package body.
A solid-body packaging approach is not appropriate for some integrated-circuit modules. An integrated-circuit module that includes a pressure sensor or optical sensor, for example, requires the use of an open-cavity package so that environmental pressure or external light sources can reach the device. However, a lid to the package is typically provided, in some cases to protect the interior parts but more generally to provide a surface that can be used by pneumatic pick-and-place machinery during the manufacture of circuit boards or other units that use the packaged devices.
FIG. 1 illustrates examples of open-cavity packages that might be used with a pressure sensor, for example. Package 110 includes a plastic package body 115 and a plastic lid 120 affixed thereto. Plastic lid 120 has a large opening in its center, to allow environmental pressure to reach a pressure sensor inside the package. Package 150 comprises a ceramic package body 155 and a metal lid 160 affixed thereto. Metal lid 160 also has an opening in the center.
During manufacture of packaged devices like those shown in FIG. 1, each lid typically is placed on the package body one at a time, using pneumatic pick-and-place machinery, and glued or welded into place. Improved processes are needed for assembling integrated-circuit modules using open-cavity packages.